Organic peroxides have long been used as free radical-forming curing agents for crosslink curable polyolefins such as polyethylene and copolymers of ethylene, as is shown by U.S. Pat. Nos. 2,628,214 and 2,826,570.
Di-tertiary butyl peroxide comprises one of many free radical-generating peroxide crosslink curing agents identified in the patent literature as suitable for crosslink curing polyolefin materials. For example, see U.S. Pat. Nos. 2,710,291; 2,919,474; 3,201,503; 3,209,055; 3,234,197; 3,257,352; 3,372,139; 3,522,222; 3,632,680 and 3,661,877. Di-tertiary butyl peroxide, moreover, constitutes a peroxide compound having several highly significant economic and other benefits with respect to its use as a crosslinking curing agent. Namely, in addition to being a relatively low cost material in relation to other organic peroxides, di-tertiary butyl peroxide is characterized by a very high ratio of active oxygen with respect to its weight, among other possible advantageous attributes. For instance, the cost of di-tertiary butyl peroxide is approximately one-half of that of di-.alpha.-cumyl peroxide which substantially constitutes the standard peroxide curing agent of the industry in uses such as the curing of polyolefins according to the teachings of U.S. Pat. Nos. 2,888,424 and 3,079,370. Moreover, di-tertiary butyl peroxide provides about twice the amount of active oxygen over that obtainable from an equal amount of weight from the commonly used di-.alpha.-cumyl peroxide.
Notwithstanding its extensive publication or mention in the patent and other technical literature, and the evident substantial economical advantages of di-tertiary butyl peroxide as a free radical-generating cross-linking agent for polyolefins over the industry standard of di-.alpha.-cumyl peroxide, di-tertiary butyl peroxide apparently possesses certain characteristics, such as high volatility and a slow rate of decomposition (long half-life), which have greatly hindered its general acceptance and use as a free radical forming crosslink curing agent for polyolefin materials in the polymer industry.
For instance, experience has shown that up to about 60 to 70 percent of this volatile peroxide added can be lost by evaporation using conventional compounding techniques and apparatus, and an article entitled "The Influence Of Peroxide Curing Systems And Carbon Blacks In Ethylene-Propylene Rubber" by Lenas, published in I&EC Product Research and Development, pp. 269 to 277, Volume 3, No. 4, December, 1964, for example, reports that from past experience with di-tertiary butyl peroxide, appreciable amounts of up to about 40 percent of the peroxide applied have been lost during compounding or mixing due to its very high degree of volatility.